Local update pof and sof relations

I am working on configuring StratixII GX with Local Update capability.

While using Coverting Programming Files Dialog box, I noticed I can choose the Programing file type to be "Programmer Object File for Local Update (.pof)". After I made the choice, The File/Data area appear with 2 rows:

POF Data - Page_0

SOF Data - Page_1

That makes me confused. I thought the factory page and application page for the Local Update scheme should be with the same type but why QuartusII asked for one pof and the other sof.

Also, later on, what format (sof or pof) should I write into the FLASH (by direct write instead of MAXII of course) before it gets configured into the FPGA.

I would appreciate very much if any one has the answer or can provide a pointer to any document that explains what exactly is in the pof or sof files.

Thanks!